The actress stars as one of a group of scientists who are trapped underwater following a devastating earthquake in Will Eubank’s upcoming action-thriller Underwater (out Jan. 10), which also stars Vincent Cassel, Jessica Henwick, Mamoudou Athie, and T.J. Miller (the film was shot in early 2017, before Miller’s fake bomb threat arrest or allegations of sexual assault and workplace misconduct came out against him). We asked Stewart about taking the plunge.

Alan Markfield/Fox

How would you describe the movie?It’s a really dark, scary meditation on isolation. Basically, it’s like a survival movie about a bunch of people that don’t know each other, and the strange, occasionally existential conversations that ensue, and the weird relationships being formed really quickly. The underlying story of [disrupting] something that really should be left in its natural state, and what you can unearth — that’s what keeps it scary.

What appealed to you about your character, Norah?I have a real protective feeling for that character and how they wrote her. There’s this fragile nature that this girl has, and you just never really know why. Information about her sort of filters out throughout the really traumatic events. That’s where you start to kind of get to know each other, and the deepest parts of yourself come out.

You wrapped production over two years ago. How are you feeling now that it’s finally hitting theaters?I’m stoked. I haven’t made a movie of this scale maybe ever. It was not an easy movie to make — really long and just drippy and cold and f—ing hard. I want to see how we all reacted in such precarious circumstances. It really pulls out the best and worst parts of people.

Alan Markfield/Fox

What were some of the biggest challenges of filming?The suits were really heavy, honestly. We couldn’t move around. I really don’t like being held down, I don’t like confined spaces, I’m not a strong swimmer. The reason that, like, huge f—ing surly dudes who typically do action movies do them is because they’re actually really hard and scary and they hurt. I think none of us in the movie — except for maybe Vincent [Cassel], who’s, like, a f—ing wild banshee — really knew what we were getting ourselves into. And that’s where there’s some comedy in the movie every once in a while; in the most dire situations you kind of laugh in a funeral. That’s kind of what it felt like to make the movie as well. Like we were all dying!